The goal of this project is the development of carefully monitored cultures of wild rodent species as experimental animals for a variety of biomedical problems. These animals are being characterized and standardized as to their physical proportions, body composition, nutrition, blood chemistry, mortality rates, and environmental requirements. The central areas of study are (1) the optimization of conditions for reproduction, growth and health so that the species may be readily maintained in captivity and (2) the identification and characterization of special features such as susceptibility to diseases common to humans (atherosclerosis, diabetes, nephritis, and mammary tumors), large or small organ proportions, high or low levels of chemical constituents, unusual resistance of susceptibility to environmental stressors, etc., which would make a given species particularly suitable for a given biomedical problem.